Gelatinase B is a member of the matrix metalloproteinase family known to play a role in tumor cell invasion and in destruction of cartilage in arthritis. The enzyme is synthesized as a zymogen and requires zinc and calcium for activity. The main objective of the proposed research is to unravel the mechanism of action of gelatinase B, in order to be able to control its activity in vivo and subsequently design specific inhibitors for the enzyme to prevent tumor invasion. Towards the achievement of this goal we have expressed the putative active site region of gelatinase B containing the zinc binding region in E. coli as a fusion protein. The fusion protein has been found to be active toward the synthetic substrate. In this study, the structure of the putative active site of the enzyme and its interaction with metal ions, Zn and Mn will be determined by ESR spectroscopy.